Many of the signal transduction pathways that regulate a variety of cellular processes, including the differentiation and proliferation of normal and malignant cells, operate through phosphorylated proteins called tyrosine kinases. The two major types of tyrosine kinases are receptor and nonreceptor tyrosine kinases.
Receptor tyrosine kinases contain binding sites or receptors for growth factors such as epidermal growth factor (EGF) or platelet-derived growth factor (PDGF). When a growth factor such as EGF or PDGF binds to the receptor, the tyrosine kinase receptor protein is activated; the tyrosine kinase receptor protein is autophosphorylated; and endogenous proteins that participate in the signal transduction pathway are phosphorlyated.
Some endogenous proteins that are involved in the cellular signal transduction pathways contain a specific domain called the SH2 domain, which provides for interaction with an activated tyrosine kinase receptor protein. This interaction is a protein-protein interaction. One protein that contains an SH2 domain is pp60c-src kinase, which is also a tyrosine kinase. The pp60c-src kinase is a nonreceptor kinase and is related to a number of nonreceptor tyrosine kinases, which include, but are not limited to, Fyn, Lck, Yes, Blk, Lyn, Fgr, Hck, and Yrk. Another important protein that contains an SH2 domain is Abl.
The pp60c-src protein is exemplary of the Src family of tyrosine kinases. The pp60c-src has three major domains: SH1, SH2, and SH3. The SH1 domain is most commonly called the catalytic domain or tyrosine kinase domain. The SH3 domain is a binding region for proteins having proline-rich sequences. Both the SH2 and SH3 domains are noncatalytic, but are important in protein-protein recognition.
The Src family of protein kinases, which all contain a SH2 domain, are involved in a number of cellular signalling pathways. For example, Src is involved in growth factor receptor signalling; integrin-mediated signaling; T- and B-cell activation and osteoclast activation. It is known that the Src SH2 domain binds to several key receptor and nonreceptor tyrosine kinases such as tyrosine kinases containing receptors for PDGF, EGF, HER2/Neu (an oncogene form of EGF), Fibroblast growth factor, focal adhesion kinase, p130 protein, and p68 protein. In addition, pp60c-src has been shown to be involved in the regulation of DNA synthesis, mitosis, and other cellular activities.
Thus, it would be useful to have compounds that inhibit the binding of proteins containing an SH2 domain to cognate phosphorylated proteins, as the inhibition of binding of proteins containing an SH2 domain to cognate phosphorylated proteins can be used to treat proliferative diseases such as cancer, osteoporosis, inflammation, allergy, restenosis, and cardiovascular disease, which all rely on signal transduction involving proteins that contain an SH2 domain that binds to phosphorylated proteins during the cellular signalling process.